Far field auditory evoked potentials can be detected on the scalp by averaging and used as a measure of neonatal auditory system development in humans and animals, and the technique is now beginning to be used as a clinical measure. Many neonatal problems have been correlated with hearing loss in humans (e.g., ototoxic drugs, hyperbilirubinemia). It should be possible to detect auditory system damage from some of these causes in the neonate, at a time when corrective action may be effective. The technique involves recording VIIIth nerve and brainstem electrical activity from surface electrodes by means of averaging the electrical responses to repeated auditory "click" stimuli. Changes in the obtained waveform can be observed during postnatal development of a single subject by repeated recordings during maturation. The test will be under the control of a digital minicomputer, which will be programmed to reduce the many artifacts that we anticipate would otherwise result in low quality recordings from high-risk infants in the intensive care nursery. The computer will also make it possible for us to obtain later (cortical) auditory evoked responses under these artifact-free conditions.